Rational combinations of Betti diagrams of complete intersections

We investigate decompositions of Betti diagrams over a polynomial ring within the framework of Boij-S\"oderberg theory. That is, given a Betti diagram, we determine if it is possible to decompose it into the Betti diagrams of complete intersections. To do so, we determine the extremal rays of the cone generated by the diagrams of complete intersections and provide a rudimentary algorithm for decomposition.Comment: This research was conducted at the Willamette Mathematics Consortium RE

Quasar Spectral Slope Variability in the Optical Band

We performed a new analysis of B and R light curves of a sample of PG quasars. We confirm the variability-redshift correlation and its explanation in terms of spectral variability, coupled with the increase of rest-frame observing frequency for quasars at high redshift. The analysis of the instantaneous spectral slope for the whole quasar samples indicates both an inter-QSO and intra-QSO variability-luminosity correlation. Numerical simulations show that the latter correlation cannot be entirely due to the addition of the host galaxy emission to a nuclear spectrum of variable luminosity but constant shape, implying a spectral variability of the nuclear component. Changes of accretion rate are also insufficient to explain the amount of spectral variation, while hot spots possibly caused by local disk instabilities can explain the observations.Comment: 20 pages, 6 figures, to appear in Ap.J., January 200

Surgical management of primary colonic lymphoma: Big data for a rare problem

Background and ObjectivesPrimary colonic lymphoma (PCL) is rare, heterogeneous, and presents a therapeutic challenge for surgeons. Optimal treatment strategies are difficult to standardize, leading to variation in therapy. Our objective was to describe the patient characteristics, short‐term outcomes, and five‐year survival of patients undergoing nonpalliative surgery for PCL.MethodsWe performed a retrospective cohort analysis in the National Cancer Database. Included patients underwent surgery for PCL between 2004 to 2014. Patients with metastases and palliative operations were excluded. Univariate predictors of overall survival were analyzed using multivariable Cox proportional hazard analysis.ResultsWe identified 2153 patients. Median patient age was 68. Diffuse large B‐cell lymphoma accounted for 57% of tumors. 30‐ and 90‐Day mortality were high (5.6% and 11.1%, respectively). Thirty‐nine percent of patients received adjuvant chemotherapy. For patients surviving 90 days, 5‐year survival was 71.8%. Chemotherapy improved survival (surgery+chemo, 75.4% vs surgery, 68.6%; P = .01). Adjuvant chemotherapy was associated with overall survival after controlling for age, comorbidity, and lymphoma subtype (HR 1.27; 95% CI, 1.07‐1.51; P = .01).ConclusionsPatients undergoing surgery for PCL have high rates of margin positivity and high short‐term mortality. Chemotherapy improves survival, but <50% receive it. These data suggest the opportunity for improvement of care in patients with PCL.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150597/1/jso25582_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150597/2/jso25582.pd

Cluster-Cluster Microlensing as a Probe of Intracluster Stars, MACHOs, and Remnants of the First Generation Stars

The galaxy cluster Abell 2152 is recently found to be forming a cluster-cluster system with another, more distant cluster whose core is almost perfectly aligned to that of A2152. We discuss the detectability of microlensing events where a single star in the source cluster behind A2152 is extremely magnified by an intracluster compact object in A2152. We show that a search with an 8m-class telescope with a wide field of view, such as the Subaru/Suprime-Cam, can probe intracluster compact objects with a wide mass range of m_{co} ~ 10^{-5}-10^{10} M_sun, including ranges that have not yet been constrained by any past observations. We expect that the event rate is biased for the background cluster than the foreground cluster (A2152), which would be a unique signature of microlensing, making this experiment particularly powerful. The sensitivity of this experiment for the mass fraction of compact objects would be 1-10% in the total dark matter of the cluster, which is roughly constant against m_{co}, with a reasonable telescope time for large telescopes (~10 nights). Therefore any compact objects in this mass range can be detected or rejected as the dominant component of the dark matter. About 10 events are expected if 20% of the cluster mass is in a form of compact objects with M ~ 1 M_sun, as claimed by the MACHO collaboration for the Milky Way halo. Other possibly detectable targets include intracluster stars stripped by galaxy interactions, and hypothetical very massive black holes (M >~ 100 M_sun) produced as remnants of the first generation stars, which might be responsible for the recently reported excess of the cosmic infrared background radiation that seems impossible to explain by normal galactic light.Comment: 14 pages, 6 figures, to appear in ApJ. Some minor corrections, and references adde

Molecular Gas in the z=1.2 Ultraluminous Merger GOODS J123634.53+621241.3

We report the detection of CO(2-1) emission from the z=1.2 ultraluminous infrared galaxy (ULIRG) GOODS J123634.53+621241.3 (also known as the sub-millimeter galaxy GN26). These observations represent the first discovery of high-redshift CO emission using the new Combined Array for Research in Millimeter-Wave Astronomy (CARMA). Of all high-redshift (z>1) galaxies within the GOODS-North field, this source has the largest far-infrared (FIR) flux observed in the Spitzer 70um and 160um bands. The CO redshift confirms the optical identification of the source, and the bright CO(2-1) line suggests the presence of a large molecular gas reservoir of about 7x10^10 M(sun). The infrared-to-CO luminosity ratio of L(IR)/L'(CO) = 80+/-30 L(sun) (K Km/s pc^2)^-1 is slightly smaller than the average ratio found in local ULIRGs and high-redshift sub-millimeter galaxies. The short star-formation time scale of about 70 Myr is consistent with a starburst associated with the merger event and is much shorter than the time scales for spiral galaxies and estimates made for high-redshift galaxies selected on the basis of their B-z and z-K colors.Comment: Accepted for publication in ApJ Letter

How Low Can We Go?: Comparing Long-term Oncologic Outcomes for APR and LAR in Very Low Rectal Cancer

Management of very low rectal cancer is one of the most challenging issues faced by colorectal surgeons. For tumors in the mid and upper rectum, procedures can be done to resect the cancer while maintaining continence, a major determinant of post-operative quality of life. In the low rectum, however, to optimize oncologic outcomes, many surgeons feel compelled to pursue abdominoperineal (APR) over low anterior resection (LAR), a sphincter-preserving procedure. It was hypothesized that after robust adjustment, procedure choice will not be associated with a difference in disease-free survival in the resection of tumors in the low rectum. To analyze this, the US Rectal Cancer Collaborative Database, a comprehensive, multi-center dataset obtained from six institutions between 2010 and 2016, was queried. Patients undergoing TME resection for Stage I-III very low rectal cancers (involvement) were selected for this study. Patients were categorized by procedure- LAR vs APR. Primary outcome was five-year disease-free survival. Secondary outcomes included overall survival, recurrence, length of stay, and complications. An adjusted analysis was performed to account for all known potential confounders. 431 patients with very low rectal cancer treated by either APR or LAR were identified. 154 (35.7%) underwent APR. The overall recurrence rate was 19.6%. Median follow-up time was 42.5 months. An analysis adjusted for age, gender, BMI, ASA class, and pathologic stage observed no difference in disease free survival between operative types (HR=0.90, 95% CI [0.53-1.52], p=0.70). Similarly, secondary outcomes demonstrated no significant difference between operation types, including length of stay (Beta: 0.04, Std. error = 0.25, p = 0.54), overall survival (HR=1.29, 95% CI [0.71-2.32], p=0.39), or complications (OR = 1.53, 95% CI [0.94 - 2.50], p=0.09). In this analysis, no significant difference in disease-free survival or overall survival was observed between patients undergoing APR or LAR for very low rectal cancer. This comprehensive study supports the treatment of very low rectal cancer, less than 5cm from the anorectal ring with no sphincter involvement, by either abdominal perineal or low anterior resection. Further studies may focus on patient-reported and quality of life outcomes which may influence decision-making

Structure Function Analysis of Long Term Quasar Variability

In our second paper on long-term quasar variability, we employ a much larger database of quasars than in de Vries, Becker & White. This expanded sample, containing 35165 quasars from the Sloan Digital Sky Survey Data Release 2, and 6413 additional quasars in the same area of the sky taken from the 2dF QSO Redshift Survey, allows us to significantly improve on our earlier conclusions. As before, all the historic quasar photometry has been calibrated onto the SDSS scale by using large numbers of calibration stars around each quasar position. We find the following: (1) the outbursts have an asymmetric light-curve profile, with a fast-rise, slow-decline shape; this argues against a scenario in which micro-lensing events along the line-of-sight to the quasars are dominating the long-term variations in quasars; (2) there is no turnover in the Structure Function of the quasars up to time-scales of ~40 years, and the increase in variability with increasing time-lags is monotonic and constant; and consequently, (3) there is not a single preferred characteristic outburst time-scale for the quasars, but most likely a continuum of outburst time-scales, (4) the magnitude of the quasar variability is a function of wavelength: variability increases toward the blue part of the spectrum, (5) high-luminosity quasars vary less than low-luminosity quasars, consistent with a scenario in which variations have limited absolute magnitude. Based on this, we conclude that quasar variability is intrinsic to the Active Galactic Nucleus, is caused by chromatic outbursts / flares with a limited luminosity range and varying time-scales, and which have an overall asymmetric light-curve shape. Currently the model that has the most promise of fitting the observations is based on accretion disk instabilities.Comment: 23 pages, 18 figures. Accepted for publication in Astronomical Journal, Feb 2005 issu

The timing of anthropogenic emergence in simulated climate extremes

Determining the time of emergence of climates altered from their natural state by anthropogenic influences can help inform the development of adaptation and mitigation strategies to climate change. Previous studies have examined the time of emergence of climate averages. However, at the global scale, the emergence of changes in extreme events, which have the greatest societal impacts, has not been investigated before. Based on state-of-the-art climate models, we show that temperature extremes generally emerge slightly later from their quasi-natural climate state than seasonal means, due to greater variability in extremes. Nevertheless, according to model evidence, both hot and cold extremes have already emerged across many areas. Remarkably, even precipitation extremes that have very large variability are projected to emerge in the coming decades in Northern Hemisphere winters associated with a wettening trend. Based on our findings we expect local temperature and precipitation extremes to already differ significantly from their previous quasi-natural state at many locations or to do so in the near future. Our findings have implications for climate impacts and detection and attribution studies assessing observed changes in regional climate extremes by showing whether they will likely find a fingerprint of anthropogenic climate change

Contributions to early HIV diagnosis among patients linked to care vary by testing venue

<p>Abstract</p> <p>Objective</p> <p>Early HIV diagnosis reduces transmission and improves health outcomes; screening in non-traditional settings is increasingly advocated. We compared test venues by the number of new diagnoses successfully linked to the regional HIV treatment center and disease stage at diagnosis.</p> <p>Methods</p> <p>We conducted a retrospective cohort study using structured chart review of newly diagnosed HIV patients successfully referred to the region's only HIV treatment center from 1998 to 2003. Demographics, testing indication, risk profile, and initial CD4 count were recorded.</p> <p>Results</p> <p>There were 277 newly diagnosed patients meeting study criteria. Mean age was 33 years, 77% were male, and 46% were African-American. Median CD4 at diagnosis was 324. Diagnoses were earlier via partner testing at the HIV treatment center (N = 8, median CD4 648, p = 0.008) and with universal screening by the blood bank, military, and insurance companies (N = 13, median CD4 483, p = 0.05) than at other venues. Targeted testing by health care and public health entities based on patient request, risk profile, or patient condition lead to later diagnosis.</p> <p>Conclusion</p> <p>Test venues varied by the number of new diagnoses made and the stage of illness at diagnosis. To improve the rate of early diagnosis, scarce resources should be allocated to maximize the number of new diagnoses at screening venues where diagnoses are more likely to be early or alter testing strategies at test venues where diagnoses are traditionally made late. Efforts to improve early diagnosis should be coordinated longitudinally on a regional basis according to this conceptual paradigm.</p

Colors of 2625 Quasars at 0<z<5 Measured in the Sloan Digital Sky Survey Photometric System

We present an empirical investigation of the colors of quasars in the Sloan Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625 quasars with SDSS photometry. The quasars are distributed in a 2.5 degree wide stripe centered on the Celestial Equator covering $\sim529$ square degrees. Positions and SDSS magnitudes are given for the 898 quasars known prior to SDSS spectroscopic commissioning. New SDSS quasars represent an increase of over 200% in the number of known quasars in this area of the sky. The ensemble average of the observed colors of quasars in the SDSS passbands are well represented by a power-law continuum with $\alpha_{\nu} = -0.5$ ($f_{\nu} \propto \nu^{\alpha}$). However, the contributions of the $3000 {\rm \AA}$ bump and other strong emission lines have a significant effect upon the colors. The color-redshift relation exhibits considerable structure, which may be of use in determining photometric redshifts for quasars. The range of colors can be accounted for by a range in the optical spectral index with a distribution $\alpha_{\nu}=-0.5\pm0.65$ (95% confidence), but there is a red tail in the distribution. This tail may be a sign of internal reddening. Finally, we show that there is a continuum of properties between quasars and Seyfert galaxies and we test the validity of the traditional division between the two classes of AGN.Comment: 66 pages, 15 figures (3 color), accepted by A